International Journal of Modern Physics B

Isotropic-genesis nematic elastomers (IGNEs) are liquid crystalline polymers (LCPs) that have been randomly, permanently cross-linked in the high-temperature state so as to form an equilibrium random solid. Thus, instead of being free to diffuse throughout the entire volume, as they would be in the liquid state, the constituent LCPs in an IGNE are mobile only over a finite, segment specific, length-scale controlled by the density of cross-links. We address the effects that such network-induced localization have on the liquid–crystalline characteristics of an IGNE, as probed via measurements made at high temperatures. In contrast with the case of uncross-linked LCPs, for IGNEs these characteristics are determined not only by thermal fluctuations but also by the quenched disorder associated with the cross-link constraints. To study IGNEs, we consider a microscopic model of dimer nematogens in which the dimers interact via orientation-dependent excluded volume forces. The dimers are, furthermore, randomly, permanently cross-linked via short Hookean springs, the statistics of which we model by means of a Deam–Edwards type of distribution. We show that at length-scales larger than the size of the nematogens this approach leads to a recently proposed, phenomenological Landau theory of IGNEs [Lu et al., Phys. Rev. Lett.108, 257803 (2012)], and hence predicts a regime of short-ranged oscillatory spatial correlations in the nematic alignment, of both thermal and glassy types. In addition, we consider two alternative microscopic models of IGNEs: (i) a wormlike chain model of IGNEs that are formed via the cross-linking of side-chain LCPs; and (ii) a jointed chain model of IGNEs that are formed via the cross-linking of main-chain LCPs. At large length-scales, both of these models give rise to liquid–crystalline characteristics that are qualitatively in line with those predicted on the basis of the dimer-and-springs model, reflecting the fact that the three models inhabit a common universality class.

We have investigated the elastic and thermal properties of Sr_1-xCa_xRuO₃(0≤x ≤1) perovskite using a modified rigid ion model (MRIM). The trend of variation of our computed specific heat in the temperature range 1 K ≤ T ≤ 1000 K are in good agreement with corresponding experimental data for almost all the compositions (x). The specific heat found to increase with temperature from 1 K to 300 K, while they decrease with concentration (x) for these perovskite ruthenates. Besides, we have reported the thermal properties, like thermal expansion (α), molecular force constant (f), Reststrahlen frequency (υ), cohesive energy (ϕ), Debye temperature (θ_D) and Gruneisen parameter (γ).

This study is focused on the effects of cosmic rays (solar activity) and halogen-containing molecules (mainly chlorofluorocarbons — CFCs) on atmospheric ozone depletion and global climate change. Brief reviews are first given on the cosmic-ray-driven electron-induced-reaction (CRE) theory for O₃ depletion and the warming theory of halogenated molecules for climate change. Then natural and anthropogenic contributions to these phenomena are examined in detail and separated well through in-depth statistical analyses of comprehensive measured datasets of quantities, including cosmic rays (CRs), total solar irradiance, sunspot number, halogenated gases (CFCs, CCl₄ and HCFCs), CO₂, total O₃, lower stratospheric temperatures and global surface temperatures. For O₃ depletion, it is shown that an analytical equation derived from the CRE theory reproduces well 11-year cyclic variations of both polar O₃ loss and stratospheric cooling, and new statistical analyses of the CRE equation with observed data of total O₃ and stratospheric temperature give high linear correlation coefficients ≥ 0.92. After the removal of the CR effect, a pronounced recovery by 20 ~ 25 % of the Antarctic O₃ hole is found, while no recovery of O₃ loss in mid-latitudes has been observed. These results show both the correctness and dominance of the CRE mechanism and the success of the Montreal Protocol. For global climate change, in-depth analyses of the observed data clearly show that the solar effect and human-made halogenated gases played the dominant role in Earth's climate change prior to and after 1970, respectively. Remarkably, a statistical analysis gives a nearly zero correlation coefficient (R = -0.05) between corrected global surface temperature data by removing the solar effect and CO₂ concentration during 1850–1970. In striking contrast, a nearly perfect linear correlation with coefficients as high as 0.96–0.97 is found between corrected or uncorrected global surface temperature and total amount of stratospheric halogenated gases during 1970–2012. Furthermore, a new theoretical calculation on the greenhouse effect of halogenated gases shows that they (mainly CFCs) could alone result in the global surface temperature rise of ~0.6°C in 1970–2002. These results provide solid evidence that recent global warming was indeed caused by the greenhouse effect of anthropogenic halogenated gases. Thus, a slow reversal of global temperature to the 1950 value is predicted for coming 5 ~ 7 decades. It is also expected that the global sea level will continue to rise in coming 1 ~ 2 decades until the effect of the global temperature recovery dominates over that of the polar O₃ hole recovery; after that, both will drop concurrently. All the observed, analytical and theoretical results presented lead to a convincing conclusion that both the CRE mechanism and the CFC-warming mechanism not only provide new fundamental understandings of the O₃ hole and global climate change but have superior predictive capabilities, compared with the conventional models.

We analyze a crucial effect of the spin-path environment on a single and maximum entangled two-qubit systems. For a single qubit, we investigate the coherent loss by means of coherent-vectors' dynamics and the interacted qubits' fidelity. We used entanglement and population dynamics to investigate the coherent loss of the two-qubit system. We show and numerically verify that the effect of the detuning and coupling parameters in the negativity can be mapped onto the maximum and minimum values of the entanglement.

The current-voltage characteristic for nanoscale MOSFET is presented based to the velocity saturation and quantum confinement. It has been clarified that the drain velocity which is saturated with an increased drain voltage limits the onset of the current saturation. In the presence of high electric field, the motion of the velocity saturation that is randomly oriented in the equilibrium becomes streamlined and unidirectional. The model presents the current-voltage characteristic from the drift-diffusion regime to the ballistic regime with the presence of the quantum confinement on the charge carrier distribution and the energy quantization. The obtained results are considered in the modeling of the current-voltage characteristics of nanoscale two-dimensional MOSFET and show good agreement with the experimental data without using any artificial parameters.

Effects of oxygen vacancy (Vo) on magnetic properties of Co-doped ZnO are investigated by first principle calculations. The calculated formation energies of Vo with different bonding to Co atom indicate that Vo prefers location near Co atom, implying a strong local interaction between the Co atom and O-vacancy. Induced by Vo, the Co-3d and O-2p valence bands upward shift towards the Fermi level, leading to the presence of additional carriers at the Fermi level. The delocalized carriers and the substitutional Co ion play a key role in the occurrence and stability of ferromagnetism of Co-doped ZnO.

The resonating mean-field theory (Res-MFT) has been applied and shown to effectively describe two-gap superconductivity (SC). Particularly at T = 0 using a suitable chemical potential, the two-gap SC in MgB₂ has been well described by the Res-Hartree-Bogoliubov theory (Res-HBT). The Res-HB ground state generated with HB wavefunctions almost exhausts the ground-state correlation energy in all the correlation regimes. In this paper we make an attempt at a Res-MF theoretical description of thermal behavior of the two-gap SC. In an equal energy-gap case we find a new formula leading to a higher critical temperature T_c than the T_c of the usual HB formula.

The first-principles calculations of the transport characteristics of 4-(5-(2-(5-(4-mercaptophenyl)thiophene-2-yl)ethyl)pyridin-2-yl)benzenethiol sandwiched between two gold leads are performed. The effect of rectification and negative differential resistance (NDR) are obtained, which promise the potential applications in the field of molecular electronics. The rectification effect is 4.49. The peak/valley ratio of the NDR effect is as large as 4.51 for the forward bias and 12.09 for the reverse bias. The strong coupling between gold lead and molecule through thiolate results in the localization of the energy states of gold lead, which may induce the effect of rectification and NDR.

This paper presents an electromagnetic wave absorbing technique to reduce a radar cross-section (RCS) of a patch array antenna without compromising their antenna performance. The technique is based on periodic patterns, which is made of resistive materials. The 2×2 patch array antenna with a resonance frequency of 3.0 GHz was designed and fabricated. To reduce the RCS of the patch array antenna, the periodic patterns using a square patch element were proposed and applied to the surface between the four antenna patches. The printed lossy periodic patterns have radar absorbing performance at 12.0 GHz frequency. The measured results show that the lossy periodic patterns have no significant effect on the antenna radiation performance. On the other hand, the RCS is reduced by more than 98% compared to the conventional antenna at the target frequency.